1. Field of the Invention
The present invention relates to a method for controlling a call reception operation in a wide area radio pager, and more particularly to such a call reception control method capable of avoiding reception errors in boundary areas.
2. Description of the Prior Art
Generally, a wide area radio pager is a radio pager which is configured so that even when the user moves from a service area originally registered for the pager to an area not registered, the same call service as in the registered area is continuously provided in the unregistered area.
The configuration of such a wide area radio pager, a call reception control method applied to the wide area radio pager, and radio call reception errors of the wide area radio pager occurring in boundary areas will now be described in conjunction with FIGS. 1 to 3.
FIG. 1 is a block diagram illustrating the configuration of a wide area radio pager.
As shown in FIG. 1, the wide area radio pager includes a receiving unit 11 for receiving a radio call signal from a base station via a receiving channel set by a desired local oscillation frequency, and a control unit 12 for automatically recognizing an area, to which the user of the pager moves, in response to the movement of the user or a key manipulation by the user, thereby outputting a control signal for controlling a reception status of the receiving unit 11. The wide area radio pager also includes a PLL synthesizing unit 13 for receiving the control signal from the control unit 12, generating a local oscillation frequency for changing the reception status of the receiving unit 11 based on the received control signal, and sending the local oscillation frequency to the receiving unit 11, and a memory unit 14 stored with channel information and area codes associated with all available areas and adapted to provide, to the control unit 12, the channel information and area code associated with the area to which the user of the pager has moved, when the control unit 12 performs a control function to recognize the area.
The control unit 12 internally includes a decoder 15 and a central processing unit (CPU) 16. When the user of the pager moves to an area, the CPU 16 reads out the channel information and area code associated with the area, to which the user has moved, from the memory unit 14, thereby generating a reception change control signal for changing a reception status of the receiving unit 11 so that the reception status meets the channel associated with the area. When the CPU 16 detects a radio call signal received at the pager under the condition in which the reception status of the receiving unit 11 has changed as mentioned above, it detects an area code carried in the radio call signal and compares the detected area code with the area code read out from the memory unit 14. Where the compared area codes are identical to each other, the CPU 16 recognizes the area represented by the detected area code as the area to which the user has moved, so that it performs a control for receiving a radio call signal in the recognized area.
The decoder 15 is enabled by a control signal generated from the CPU 16 after the CPU 16 recognizes the area to which the user has moved. In the enable state, the decoder 15 decodes the radio call signal received at the receiving unit 11. When the decoder 15 detects an address associated therewith from the decoded signal, it sends message information included in the decoded signal to the CPU 16.
Such a call receiving procedure carried out in the above-mentioned wide area radio pager is illustrated in FIG. 2. Now, the call receiving procedure will be described in detail in conjunction with FIG. 2.
In order for the wide area radio pager to perform a wide area call service, the memory unit 14 is previously stored with channel information and area identification (ID) codes associated with all available areas.
When the radio pager turns on in accordance with an application of power thereto, variables of all functional units of the radio pager including the CPU 16 are initialized (Step 20). Initially, the receiving channel of the radio pager is set by the channel of a service area originally registered for the radio pager. In this state, the radio pager performs an operation for receiving a radio call signal (Step 21).
Where no radio call signal is detected via the initially set receiving channel for a predetermined period of time from a point of time when a radio call signal has been received via the receiving channel, such a non-reception results from a situation in which the radio pager is positioned in a poor reception area, a situation in which there is a failure in the base station associated with the radio pager, or a situation in which the radio pager has moved to an area not registered. When it is determined that the radio pager has moved to an area not registered, in accordance with a desired determination procedure (Step 22), it is determined whether the area recognition mode of the radio pager set by a manipulation switch unit included in the radio pager corresponds to an automatic mode or a manual mode (Step 23).
Where the area recognition mode is in an automatic mode, the CPU 16 reads out channel information associated with the recognized area and area information, namely, area ID codes associated with the channel information, from the memory unit 14 in accordance with a predetermined read-out order and sets the information therein (Step 25). The CPU 16 also controls the PLL synthesizing unit 13 so that the PLL synthesizing unit 13 is tuned to the channel read out from the memory unit 14 (Step 26). Subsequently, the CPU 16 determines whether or not a radio call signal is received via the set channel (Step 27). When the a radio call signal received via the set channel is detected, the CPU 16 extracts area information, namely, an area ID code, from the detected radio call signal. The CPU 16 then determines whether or not the extracted area ID code corresponds to the area ID code read out from the memory unit 14 (Step 28).
When it is determined at step 28 that the area ID codes are different from each other, the procedure returns to Step 25 so as to read out a next channel determined in accordance with the above-mentioned read-out order. When the area ID codes correspond to each other, the CPU 16 determines that the area represented by the extracted area ID code corresponds to the area to which the user has moved (Step 31). In this case, the CPU 16 changes the reception status of the radio pager so that the radio pager receives a radio call service in the newly determined area. Under this condition, the radio pager waits for the reception of a radio call signal in the newly determined area (Step 32).
On the other hand, where it is determined at step 27 that there is no radio call signal received via the set channel, the procedure returns to step 25 so as to read out channel information associated with a next area and area ID codes associated with the channel information. Thereafter, it is repeatedly determined whether or not a radio call signal is received via a newly set channel Where there is no radio call signal until a period of time set to perform the signal reception determination procedure for all channels elapses (Step 29), this signal non-reception does not result from a situation in which the radio pager has moved to an area not registered, but results from a situation in which the radio pager is positioned in a poor reception area or a situation in which there is a failure in the base station associated with the radio pager. In this case, accordingly, the signal reception disable situation is displayed on a display unit included in the radio pager. The receiving channel of the radio pager changed on the basis of the area movement of the radio pager is recovered to the channel set just before the area movement of the radio pager is determined (Step 30). A return procedure is then executed.
Meanwhile, where it is determined at step 23 that the area recognition mode is in a manual mode, the CPU 16 recognizes the area and manually set by the user as the area to which the radio pager has moved (Step 24). The receiving channel of the radio pager is then changed so that it is set by a channel used in the area to which the radio pager has moved. After the channel change, the radio pager waits for the reception of a radio call signal in the newly set area (Step 32).
After newly setting the receiving channel by the channel of the area automatically or manually recognized as a new area, the radio pager waits for the reception of a radio call signal in the newly set area. When a radio call signal is received at the radio pager, CPU 16 determines whether or not the decoder 15 detects a synchronous code included in the received radio call signal (Step 33). Where a synchronous code is detected from the radio call signal, the decoder 15 extracts address information from a frame following the synchronous code and determines whether or not the extracted address corresponds to the address associated with the radio pager (Step 35). When the extracted address corresponds to the address of the radio pager, the radio call signal is associated with the radio pager. In this case, the decoder 15 informs the CPU 16 of the fact that the received radio call signal is associated with the radio pager. The CPU 16 then receives and processes message information included in the radio call signal, thereby generating an alarm by a driving unit included in the radio pager while displaying call information by the display unit. (Steps 36 and 37). For reception of a subsequent call signal, the procedure returns to step 33 at which it is determined whether or not the decoder 15 detects a synchronous code.
On the other hand, when no synchronous code is detected by the decoder 15 for a predetermined period of time, it is determined whether or not an area movement of the radio pager occurs (Step 34). Where there is no area movement of the radio pager, the procedure returns to step 33 to determine whether or not a synchronous code is detected. Where there is an area movement of the radio pager, the procedure returns to step 23 at which the area recognition mode of the radio pager is determined. Also, where it is determined at step 35 that the address extracted after the detection of the synchronous code does not correspond to the address associated with the radio pager, the procedure returns to step 33 to determine whether or not a synchronous code for the reception of a subsequent signal is detected.
Typically, the wide area radio pager having the above-mentioned configuration while using the above-mentioned call reception control method uses a radio call transmission system which transmits a radio call signal having a data format (FIG. 4A) according to the POCSAG protocol.
Recently, a new protocol has been proposed which provides a radio call data format capable of enabling a variety of additional services. This protocol is called a "FLEX protocol". In order to process a radio call signal according to the FLEX protocol, it is necessary to provide an A/D converter 17 between the receiving unit 11 and decoder 15 in the case of FIG. 1. Since FLEX data output from the receiving unit 11 is an analog signal having four or two levels, the A/D converter 17 performs a function for converting the analog signal into 2-bit digital data.
Since the call reception control method used in this case is carried out in accordance with a procedure for processing a variety of additional services, its call reception control procedure for executing a wide area service function is basically identical to that using the POCSAG data format, even though the data format used therein is different from the POCSAG data format.
Meanwhile, when a wide area radio pager having such a configuration is positioned in a boundary area between two adjacent areas in which radio call signals respectively transmitted from the base stations of both the adjacent areas exist in a simultaneous manner, it may receive either of the call signals. In other words, where the radio pager is positioned in a boundary area between two adjacent areas one being an area where the radio pager is currently positioned while the other area being an area adjacent to the current area of the radio pager, in a state in which the radio pager is set by a channel associated with the current area of the radio pager, it may receive a call signal generated in the area adjacent to the current area thereof. In this case, the current position of the radio pager is erroneously determined.
This will be described in detail in conjunction with FIG. 3.
FIG. 3 is a schematic view illustrating a generation of reception errors in boundary areas. In FIG. 3, the reference characters A, B, C and D represent areas in which call services are provided through different channels, respectively. The reference numeral 41 to 45 represent boundary areas among adjacent areas, respectively. In each boundary area, radio call signals respectively transmitted from the base stations of the adjacent areas associated with the boundary area exist in a simultaneous manner.
First, it is assumed that the area A is an area originally registered for a call reception service of the wide area radio pager. Where the user of the radio pager moves from the area A to the area C, he may be temporarily positioned in the boundary area 42 between the areas B and C, the boundary area 44 between the areas C and D or the boundary area 45 among the areas B, C and D.
In accordance with the above-mentioned conventional wide area radio call reception control method, the CPU 16 of the radio pager reads out information about channels respectively associated with all available areas and executes a receiving channel change operation while using those channels one by one. Where the user is positioned in the boundary area 42 between the area B and C, the radio pager can detect a radio call signal under the condition in which the receiving channel thereof is newly set to the channel associated with the area B in accordance with a channel change. In this state, the radio pager also can recognize the area B represented by area information received via the newly set channel as the current position of the user. Thus, the receiving channel of the radio pager is automatically set to the channel associated with the area B. However, radio call signals associated with the radio pager are transmitted via the channel associated with the area C because the user already informed an associated communication company of the fact that the destination to which the user moves is the area C. As a result, the radio pager, which has been automatically set by the channel associated with the area B as mentioned above, can not receive call signals transmitted via the channel associated with the area C. In other boundary areas, such a reception error occurs.
In order to solve such a problem, another method has been proposed. In accordance with this method, when an area movement of the user occurs, the wide area radio pager finds all channels through which call signals are received. Among the found channels, that exhibiting a maximum electric field strength is determined as the channel of the area to which the radio pager moves.
However, this method still have the above-mentioned problem. That is, the channel associated with an area adjacent to a destination area may exhibit an electric field strength higher than that of the channel associated with the destination area in a boundary area between the adjacent areas. In this case, reception errors may be generated. Consequently, it is impossible to completely eliminate reception errors occurring in boundary areas, using this method.